In wireless communication systems which use relay stations (“RS”), base station (“BS”) to RS transmissions, i.e. Relay-Link, and BS or RS to mobile station (“MS”) transmissions are separated in time to avoid interference and provide effective transmissions. The separate zones are called R-Zones. This zone configuration is communicated to the RSs by the BS.
Currently, relay communication systems use a relay location field in the Relay Frame Control Header (“R-FCH”) to indicate the R-Zone of the next frame to the RS. The relay location field contains an offset value in number of symbols.
When traffic load among RSs in a wireless communication system experiences rapid variations, such as a communication system operating as defined by the Institute of Electrical and Electronics Engineers (“IEEE”) standard 802.16j, relay zone locations and corresponding sizes need to be updated frequently and dynamically, resulting in significant delay and significant overhead. For a two-hop system, a change in the relay zone can be done dynamically by changing the symbol offset. In other words, the configuration can be changed starting from the next frame without any ambiguity and without impacting the operation.
However, in the case of multi-hop transmission, when the scheduling is done in distributed manner, i.e. the relays are free to assign transmissions in specified zones, a change informed by the BS cannot be propagated down to the next hop relays without misalignment of the zone configurations. For current 802.16j solutions, R-Zone location indicates the offset relative to the frame start preamble for the first Orthogonal Frequency Division Multiplexing (“OFDM”) symbol of the R-FCH or R-MAP allocation. Whenever the frame configuration is updated, the subordinate RSs do not have sufficient time to update their scheduling before and after the new configuration is effective.
For example, assume an R-zone location for a current frame is indicates an offset of 10 for the first OFDM symbol and the first RS begins its UL-MAP at an offset of 15. If the R-zone location is changed in the FCH to indicate an offset of 18, a conflict occurs between the new R-zone region and the UL allocation region because the RS does not have time to implement the change. In other words, the BS wants to transmit to the RS in a region where the RS had planned to receive data from an MS.
One prior solution provides an action frame number field in the FCH. The action frame number indicates in which upcoming frame the R-zone location change is to be implemented. Providing an action frame number requires an additional field in the FCH and introduces additional overhead. However, in the 802.16j system, as proposed, there is not enough bit space in the FCH message to insert an additional field.
Therefore, what is needed is a system and method for dynamic zoning changes in a multi-hop relaying system that allows sufficient time for multi-hop relays to implement without adding additional overhead.